In a wireless communications system, e.g. a cellular system, the channel conditions are an important consideration in the operation of the wireless system. Within a wireless communications system, a base station (BS) communicates with a plurality of wireless terminals (WTs), e.g., mobile nodes. As a wireless terminal moves to different locations within the base station's cell, the condition of the wireless communication channel between the base station and the wireless terminal may change, e.g., due to varying levels of noise and interference. The noise and interference experienced by the wireless terminal's receiver may include background noise, self-noise, and inter-sector interference. The background noise may be classified as independent from the base station's transmission power level. However, the self-noise and inter-sector interference are dependent on the base station's transmission power level, e.g. the transmission power in one or more sectors.
One method typically used to evaluate the condition of the communication channel is for the base station to transmit pilot signals, which are signals typically transmitted on a small fraction of the transmission resource and are generally comprised of known (pre-determined) symbols transmitted at a single constant power level. The wireless terminal measures the pilot signals and reports to the BS in the form of a scalar ratio such as signal-to-noise ratio (SNR) or an equivalent metric. In the case where noise/interference is not dependent on the transmitted signal, e.g., background noise is predominant and the contribution from self-noise and inter-sector interference is insignificant, such a single scalar metric is sufficient for the BS to predict how the received SNR, at the wireless terminal, will change with signal transmit power. Then, the base station can determine the minimum level of transmission power required to achieve an acceptable received SNR at the wireless terminal, for the particular error-correcting coding scheme and modulation used. However, in the case where the total noise/interference includes a significant component that is dependent on signal transmission power, e.g., inter-sector interference from base station transmissions in adjacent sectors, the commonly used technique of obtaining an SNR from pilot signals of one fixed strength level is insufficient. In such a case, the information obtained, e.g., SNR at a single transmission power level, by this commonly used technique, is insufficient and inadequate for the BS to accurately predict the received SNR at the WT as a function of the signal transmit power. Additional channel quality information needs to be generated, collected by the wireless terminal, and relayed to the base station, so that the base station can solve for the wireless terminals' function relating received SNR to base station signal transmission power level. By obtaining such a function for a wireless terminal's communication channel, the base station's scheduler, knowing the acceptable level of received SNR for a particular coding rate, error-correcting code, and modulation used, could efficiently assign a wireless terminal segments in a channel with an appropriate power level, thus achieving acceptable SNR, limiting wasted transmission power, and/or reducing overall levels of interference.
Based upon the above discussion, it is clear that there is a need, particularly in the case of multi-sector wireless communications systems, for new and novel apparatus and methods of channel quality measuring, evaluating and reporting that will provide the base station with sufficient information to obtain the wireless terminal received signal SNR as a function of base station transmitted power. In addition, to support improved and/or more diverse channel quality measurements, new pilot signal patterns, sequences and/or pilot signal transmission power levels which can facilitate the analysis of self noise and interference form other sectors of a cell are desirable.